1. Field of the Invention
The invention relates to an angular contact ball bearing with a non-contact seal member having a counterbore formed on an outer ring which is used in a spindle or the like for motors or machine tools which are required to operate at higher speed or exhibit a prolonged life, and a grease-lubricated angular contact ball bearing with a seal member, which is used for rotatably supporting the spindle. Further, the invention relates to a spindle device for machine tool with the angular contact ball bearing.
2. Description of the Related Art
Bearings for the spindle of machine tools are mostly lubricated with grease from the standpoint of cost or because such a lubrication system is free from maintenance. The spindle of machine tools have been required to operate at higher rotating speed from the necessity of meeting the requirements for higher productivity. To this end, bearings have been required to operate at higher rotating speed.
In particular, when an angular contact ball bearing having a counterbore formed on the outer ring operates at a high rotating speed while being lubricated with a grease, the base oil (lubricant) of the grease can be easily discharged due to the presence of the counterbore on the outer ring, deteriorating the retention of the lubricant in the races and hence causing mallubrication. This is disadvantageous in the durability of bearing.
When an angular contact ball bearing comprising a non-contact seal member merely mounted in the vicinity of both the axial ends of the outer ring operates at a high rotating speed, the grease in the bearing moves toward the axial ends and then is attached to the sealed portion. Although the grease itself cannot be scatted from the interior of the bearing, the base oil can be little supplied from the grease attached to the sealed portion back into the races. Thus, this type of angular contact ball bearing is insufficient in the elimination of defective grease lubrication.
In order to solve these problems, the angular contact ball bearing disclosed in Japanese Patent Laid-Open No. 1999-108068 has a grease storing groove machined on the inner surface of the outer ring so that a contact area (contact ellipse) of the outer ring race with the balls can be provided even if no non-contact seal members are mounted. In this arrangement, the base oil (lubricant) can be supplied from the grease accumulated in the storing groove back into the races, making it possible to prolong the life of the bearing as compared with the conventional bearings.
However, the angular contact ball bearing disclosed in the above cited Japanese Patent Laid-Open No. 1999-108068 is disadvantageous in that when dmN (permissible rotating speed) is as high as not lower than 1,000,000, the grease storing groove formed on the inner surface of the outer ring is not enough to inhibit the scattering of the grease accumulated in the bearing, making it difficult to make sufficient use of the grease accumulated in the bearing and hence allow the grease to contribute to lubrication.
Further, it is necessary that a grease storing groove be machined on the inner surface of the outer ring every individual bearing, preventing the reduction of production cost.
In addition, FIG. 16 is a sectional view of essential part of a conventional sealed angular contact ball bearing. The angular contact ball bearing 100 comprises an outer ring 101 having an outer ring race 101a formed on the inner surface thereof, an inner ring 103 having an inner ring race 103a formed on the outer surface thereof and a plurality of steel balls 105 disposed as rolling elements between the outer ring race 101a of the outer ring. 101 and the inner ring race 103a of the inner ring 103. The plurality of balls 105 are peripherally retained at intervals by an annular cage 106 disposed between the inner surface of the outer ring 101 and the outer surface of the inner ring 103. Further, non-contact type seals 109, 110 are mounted on the opening of both the ends of the outer ring 101 and the inner ring 103.
A shoulder portion 102 is formed at one side of the outer ring race 101a on the inner surface of the outer ring 101. On the outer surface of the inner ring 103 is formed a shoulder portion 104 symmetrically with the shoulder portion 102 of the outer ring 101 about the ball 105. By thus providing the outer ring 101 and the inner ring 103 with the shoulder portions 102 and 104, respectively, the angular contact ball bearing 100 can receive the radial load as well as the axial load.
The cage 106 is formed annually by a phenolic resin and has a plurality of cylindrical pockets 107 disposed peripherally for receiving and retaining the balls 105. The outer diameter of the cage 106 is formed slightly smaller than the inner diameter of the shoulder portion 102 of the outer ring 101. The inner diameter of the cage 106 is formed greater than the outer diameter of the shoulder portion 104 of the inner ring 103.
There is formed a small guide gap 108 between the outer surface of the cage 106 and the inner surface of the shoulder portion 102 of the outer ring 101. The grease is injected into the guide gap 108 to lubricate the cage 106 with respect to the outer ring 101.
However, the conventional sealed angular contact ball bearing 100 as shown in FIG. 16 is disadvantageous in that since the cage 106 is supported guided by the outer ring 101, the cage 106 undergoes self-excited vibration that causes the generation of abnormal noise when the guide gap 108 runs out of grease upon high speed rotation of the bearing 100.
Further, since the inner surface of the outer ring 101 and the outer surface of the cage 106 in the guide gap 108 come in contact with each other, the rise in the rotating speed of the bearing 100 is accompanied by the rise in the heat generation due to friction, causing a temperature rise.
In order to solve this problem, it can be proposed that a snap cage guided by rolling elements for use in deep groove ball bearing be used. This approach causes no generation of friction between the cage and the inner and outer rings but is not suitable for angular contact ball bearings, which have many balls incorporated therein, because such a snap cage has an insufficient strength.
In general, an angular contact ball bearing is used to support the spindle for machine tools which is required to rotate at a high precision. When the aforementioned conventional sealed angular contact ball bearing 100 is mounted on the spindle for machine tools, the temperature of the bearing rises due to self-excited vibration or friction of the cage 106 during the high speed rotation of the spindle, lowering the machining precision of machine tools.
Further, when the machine tools operate, the generation of noise increases due to the generation of abnormal noise by the cage 106.